1. Field of the Invention
The present invention relates to a digital camera, and in particular, to a digital camera equipped with an autofocus (AF) function which automatically carries out focal point adjustment.
2. Description of the Related Art
Digital cameras have become more popular in recent years. A digital camera photographs, as a still image or a dynamic image, a subject by using a solid-state image pickup system formed to include a solid-state image pickup element such as a CCD (charge coupled device) sensor or the like which picks up the subject. Such a digital camera is usually equipped with a lens system for imaging the subject onto the solid-state image pickup element. The lens system is structured to include a zoom lens which is formed by a plurality of lens groups, and a focus lens which focuses the subject which is the object of photographing.
When the power of the digital camera main body is off, the zoom lens and the focus lens of the lens system are brought together compactly and stored within a lens barrel which sinks into a case. Here, when the power of the digital camera main body is turned on, the lens barrel is extended to a predetermined reference position. Due to this extending of the lens barrel, the zoom lens and the focus lens are moved to predetermined positions within the space formed within the case, and are set in a standby state so as to await photographing (photographing standby state).
When a subject is photographed, by changing the focal length of the lens system by driving the zoom lens, the range of the photographing angle (the angle of field) can be set to a desired angle. Further, the focus position, at which the subject is in a focused state, is searched for (AF searching), and focus control for moving the focus lens to this focus position is carried out automatically (the AF function). This AF function is carried out at the point in time when the user depresses the release button halfway when photographing a subject. In this way, the subject corresponding to the AF frame provided within the finder is set in a focused state (AF locking), and a state in which it is possible to photograph a good image is set.
When taking a photograph by using a digital camera such as that described above, in order to not miss the chance for a good shot, it is preferable that the AF control processing time, which is the period of time from after the release button is depressed halfway until AF locking on the subject is carried out and a state in which photographing is possible arises, is made as short as possible.
In order to shorten the AF control processing time, a conventional technique has been proposed in which the search starting point, the searching direction, the search range, the method of judging focussing, and the like of the AF search are set in accordance with the photographing mode of the digital camera (refer to Japanese Patent Application Laid-Open (JP-A) No. 2001-208959 for example).
However, in the AF control in the aforementioned conventional technique, there are cases in which the chance for a good shot is missed due to the fixing of the focus position not being carried out in time for the desired shot. Thus, it cannot be said that the AF processing performance with respect to a subject at the time of photographing is satisfactory.